Large, endless vertical conveyors which transport a plurality of cradles or pans from a loading/unloading station to storage locations require that the pan be maintained in a uniform orientation while transisting around the conveyor path. This is only possible if the conveyor pans are pivotally mounted to the conveyor chains, as disclosed in U.S. Pat. Nos. 2,773,609 to Holappa and 3,656,608 to Lichti. One resulting disadvantage of the pivotal support system is that the conveyor pans and their supporting arms must have a great deal of play and must be capable of flexing a number of inches in any direction. While this amount of play has no adverse effect when the pans are in a storage position, this amount of play cannot be tolerated when the pan is in the loading/unloading position. In this regard, it is noted that conveyors of the type disclosed in the two aforementioned patents are for simultaneously storing 20 to 30 objects or more that are as big as automobiles. Exemplary specifications for a conveyor having this type of capacity include a height of over 85 feet and a weight of 44 tons. These conveyors typically can store a total weight of over 33 tons with each conveyor pan capable of holding over 3,000 pounds.
A conveyor of the aforedescribed magnitude which transports a load such as an automobile from a storage position into the loading/unloading position must have sufficient tolerances at the loading/unloading position to permit a loaded pan to swing and to yaw, pitch, and roll as the pan is conveyed into the loading/unloading position in order to prevent damage to the conveyor supporting structure. On the other hand, when automobiles are driven onto or off a conveyor pan, there must either be small clearances between the conveyor pan and the loading/unloading platform or the pan has to be stabilized or immobilized at the loading/unloading location.
In an automobile parking tower similar to the type depicted in the aforementioned Lichti patent and also depicted with different improvements or in different embodiments in the following U.S. Pat. Nos. 3,278,052; 3,424,321; 3,547,281; and 3,627,110 to Lichti; a very simple, rotatably mounted hemispherical steel bumper or roller which had a vertical axis of rotation was employed on either side of the conveyor pan. A pan conveyed to the loading/unloading position, was stopped in between and spaced from the two rollers. When an automobile was driven onto a pan, the pan would deflect and bang up against the forward roller. In the course of the automobile moving onto the pan and leaving the pan, the pan typically would oscillate back-and-forth a number of times striking the front and rear rollers. This not only resulted in a very noisy operation, it also seriously dented the edges of the pan. In addition, because of considerable play between the pan and the rollers, during conveyance of the pans, the pans would typically bang against one or the other roller when entering and leaving the loading/unloading station.
Other, unsuccessful attempts to satisfactorily immobilize conveyor pans can be found in several United States patents. In U.S. Pat. No. 2,645,367 to Stabile, two slide plate members 121 are suspended by springs 122 from the floor of the apparatus and provide balance as the conveyor pans or carriers 48 slide therealong. Since plates 121 do not engage the sides of carrier 48, no lateral stability is provided to the carriers when they are in the loading/unloading position. The aforementioned Holappa Patent does not even disclose a pan stabilizing means though it is conceivable that spring-biased wheels 112 on car pan 44 might steady the pan. However, the principal purpose of wheels 112 is to lower the ramp from the pan on engagement of wheels 112 with the ground.
A different approach to solve the problem of pan stability in the loading position is disclosed in the Hodous U.S. Pat. No. 2,817,446 and the Zaha U.S. Pat. No. 2,856,081 in which each pan is provided with rollers or wheels which may engage side rails. By using stabilizing means on each pan, this approach is redundant and very costly, and yet it still does not provide a quiet operation.
In some installations, it is necessary for the pan not only to be stabilized quickly, but also to be substantially coplanar with the approach ramp when stabilized. This requirement necessitates that if pan end stops are used, they be located below the top surface of the approach ramp.
In summary, none of the aforedescribed prior art devices provide an effective, quiet, inexpensive, simple, maintenance-free immobilizing means for a conveyor pan when the pan is stationary and being loaded, yet can be easily knocked out of the way when the conveyor is operating and the conveyor pans are moving past it.